Artists had made 'plein-air' or open-air studies of the sky since the 17th century. It was recommended practice that artists should sketch the changing patterns in the sky at several times of day and in various weather conditions, in order to capture it in all its moods. Here Cels has painted billowing clouds against a blue sky, with two birds wheeling in the breeze.

The inscription on the reverse indicates that the pigment was thinned with a kind of turpentine.